Disodium pamidronate.

The title compound, disodium 3-ammonium-1-hydroxypropylidene-1,1-bisphosphonate pentahydrate, 2Na(+).C(3)H(9)NO(7)P(2)(2-).5H(2)O, is used for the diagnosis and treatment of a number of bone disorders. In the solid state, disodium pamidronate shows zwitterionic character and has four different modes of chelation to sodium. The metal is octahedrally coordinated by zwitterion and water O atoms. Both coordination to sodium and hydrogen bonding determine the packing in the crystal, which comprises columns lying parallel to the crystallographic a axis.